There is nothing more beautiful in science than the eureka moment, that moment in which you find the interpretation of results, the formula or the model that explains a phenomenon, and suddenly everything makes sense. To arrive at these results, science follows a method, which could be simplified in that an observation is made, a hypothesis is formulated that tries to explain that observation, experiments are carried out and, if the experiments confirm that hypothesis, laws, equations are formulated , formulas or models, and if not, the initial hypothesis is discarded and another is sought. Best of all, once the laws are established and how the phenomenon works, those same laws allow us to make predictions. For example, thanks to Newtonian mechanics and Kepler’s laws we were able to predict the existence of the planet Neptune before it was discovered. And in science there is nothing more beautiful than an experiment confirms an experimental prediction.
One of the discoveries that follow the guidelines set by the scientific method is that of black holes. In 1789, the clergyman and geologist John Michell sent a letter to the Royal Society in which, based on Newton’s laws, he predicted the existence of objects so dense that not even light could escape from them, and in fact calculated that a body with a density 500 times greater than that of from the Sun would catch all the light and, therefore, would be invisible. The French Astronomer Pierre-Simon LaplaceA decade later, he arrived at a similar intuition. In 1915, Einstein published the theory of general relativity that explains how gravity works. This theory is read by the physicist Karl Schwarzschild, who while he was in the trenches participating in the First World War discovered that within the framework of these equations there was the possibility of producing accumulations of mass that produced a gravity so high that nothing could escape from them, not even light. However, for a long time it was thought to be nothing more than a mathematical curiosity, and not a physical reality.
There is nothing better than saying that something is impossible to exist, but that it is mathematically possible, to pique the curiosity of many scientists. In 1930, Subrahmanyan Chandrasekhar showed that, from a certain mass, called critical mass, a collapse could occur due to gravity and that no force would be able to counteract it. It was given a name with little hook, “star with a complete gravitational collapse”, although it coexisted with other names such as dark star, spherical singularity or frozen star, the latter name used by astronomers in the Soviet Union. In 1969, during a meeting of cosmologists in New York, John Wheeler coined the name black hole. Although it is not clear what the inspiration was, it seems to refer to the “black hole of Calcutta”, a dungeon in which the Hindus held British prisoners in overcrowded conditions in 1756, which caused the death of many of them.
As our knowledge about the life cycle of stars increased, it became clear that black holes are a physical reality. The discovery of pulsars, which would be star collapses, but have not reached enough mass to be a black hole, continued to argue that we were talking about a physical reality that existed in the universe and not a mere mathematical speculation. Then we were able to detect the gravitational lensing effect that a black hole produces because its immense gravity is capable of deflecting starlight in the same way that a glass lens deflects sunlight. And finally, in 2019, we had the first image of a black hole. Specifically, the one located in the center of the galaxy M87, which has about 6,500 times the mass of our Sun. It should be said that a black hole, by definition, is invisible since light does not escape from it. But we can see the shadow of the hole between the photons and the hot gas at the center of the galaxy. So 100 years later, what was a solution to Einstein’s equations has just become a physical reality, proving that the predictions were correct. Is there greater beauty in the universe than to wait serenely for 100 years to confirm a mathematical model? —Eps
JM Mulet is Professor of Biotechnology.